package myHomework;

import java.util.Scanner;

//求n以内的奇数和
public class Work2 {
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        int n=scanner.nextInt();
        int sum=0;
        for(int i=1;i<=n;i+=2){
            sum+=i;
        }
        System.out.println("sum="+sum);
    }

}
